1. Field of the Invention
Photovoltaic modules, which convert sunlight into electrical power, are available in the form of thin sheets of a rigid material, such as glass, plastic, metal, or some combination of these, that typically measure one to four feet in width and four to six feet in length. A number of such modules typically are formed into panels and mounted onto the roof of a building, and the electrical outputs of the panels are combined and processed before being used on site or fed into the electrical power grid. The present invention is an improved structure for mechanically affixing the modules to the roof of a building.
2. The Prior Art
In German Publication DE 3,247,469 A1 published Jul. 19, 1984, Melchior describes a way of mounting solar panels to a roof, in which the roof is first covered by aluminum foil. A number of parallel, spaced, upwardly inclined laths are affixed to the roof, and the solar panels are then laid down over the laths. The laths are not hollow and appear to be composed of wood. The space between the laths is bounded below by the foil-covered roof and above by the solar panels, whereby an ascending passage is formed. Air flows through the passage cooling the solar panels to improve their efficiency. To permit the cooling air to flow freely, the passages, and any electrical components in them, must remain open to the weather. Also, each panel must be connected to a common ground bus.
In U.S. Pat. No. 5,505,788 issued Apr. 9, 1996 to Dinwoodie, there is shown a roof mounting system comparable to that of Melchior; however, the laths of Melchior are replaced by any of a variety of solid pre-formed spacers, pedestals or supports. As with Melchior, the power-conducting wires and the grounding wires would be exposed to the weather.
U.S. Pat. No. 4,189,881 issued Feb. 26, 1980 to Hawley and U.S. Pat. No. 5,092,939 issued Mar. 3, 1992 to Nath et al. show how photovoltaic modules can be incorporated into a type of roof construction known as batten-seam construction. In each, a photovoltaic module is shown contained in the pans, between the battens, and this imposes a width limitation on the modules. Hawley teaches running the wires through the space enclosed beneath the battens.
In U.S. Pat. No. 4,760,680 issued Aug. 2, 1988 to Myers, there is shown a type of lap joint for use in making gratings. Because the beams are solid there is no suggestion of using them to enclose electrical wiring.
Thus, although a number of systems exist for attaching photovoltaic modules to roofs, none of these systems has a structure comparable to that of the present invention, from which a number of advantages flow, as will be described in detail below.
Roof attachment structures for photovoltaic power systems are an often-overlooked aspect of system design and system cost, but the roof attachment system is in fact one of the most important aspects in terms of liability in the event of water leakage or the loss of structural integrity. Additionally, roof attachment is the most labor-intensive step in the installation of a photovoltaic power system, and therefore, improvements in the ease of attachment will have a great impact on the total life cycle cost of a system. Statistics based on field experience confirm that there is much room for improvement in structures used to affix photovoltaic modules to the roof of a building.
With these needs in mind, the present inventors set out to develop an improved roof mounting system, which will be described below. It is believed that, compared with earlier systems, the structure of the present invention is lighter in weight, easier to install, and less susceptible to structural failure and to water damage.